Regular expressions have some standardization, but unfortunately, are often (at leart partially) implementation specific. Since you are new to the forum and AkelPad, you may not yet have discovered the User's Manual (i.e. Documentation) - I have an appendix on regular expressions, as implemented in AkelPad. Have a look there, re: your issue and I will have a look at it later also.

I am in love with AkelPad and its features and use it every day, although I don't consider myself a power user. You may also note that the (sometimes heavy) activity on the forum - especially for the Scripts plugin - indicates an active project.

rd83667,
seems you have found a bug that needs to be fixed.
Regular expressions were presented in AkelPad just few minor versions ago (officially in 4.7.4), so currently there can be some issues with their implementation. Anyway, regular expressions are much better in currently developed AkelPad 4.8.0 which latest developer's snapshot can be found at http://akelpad.sourceforge.net/files/AkelPad.zip
Additionally you can report to the "Bug reports" topic which is monitored by Instructor (the developer) regularly.